1. Field of the Invention
The present invention is related to optical shutters, and is specifically related to a precision controlled optical shutter for industrial and scientific applications.
2. Background
Optical shutters are used to switch the transmission of light on and off. Controlling light exposure in a camera is the most widespread and best-known shutter application, and the art associated with camera shutters is highly evolved to meet the specific needs of that use.
Shutters are also used in a wide range of other applications. Optical shutters used in scientific or industrial applications, hereinafter referred to as industrial shutters, are typically electronically controlled. Electronically controlled or actuated mechanical industrial shutters have been widely used in various optical applications for decades. They act quickly, they can be driven by simple electronics, and can be made quite thin. Industrial shutters generally give better light transmission when open, and better light attenuation when closed than other means of controlling light. Industrial shutters may be used to control transmission of light from a lamp or other source, or to protect sensitive materials from excess exposure to light. Such shutters are widely used in microscopy, for example, to control bleaching of dyes or pigments due to light exposure, or to select between multiple light sources or light paths, such as transmitted light versus fluorescence excitation.
Camera shutters are highly specialized and are generally designed as part of an integrated camera system, all the parts of which are designed to function together in a single application. On the other hand, industrial and scientific shutters are designed and sold as stand alone items which may used in a variety of applications by end users and, therefore, must be highly versatile and robust. Thus, the design and use of industrial shutters is significantly different than camera shutters.
The typical electronically controlled or actuated mechanical industrial shutter comprises a solenoid linked to one or more vanes that move into or out of a light path when the solenoid is activated. Normally, the solenoid action is opposed by a return spring, so that the vanes will return to a resting position when the current through the solenoid coil is turned off. The linkage of the solenoid to the vanes may be designed so that the solenoid acts either to open or to close the shutter. Such shutters are restricted to either fully open or fully closed positions.
In many industrial and scientific applications it is critical to provide very quick switching times, i.e., the time required to open or close the shutter. In order to obtain a fast open or close time, industrial shutters the vanes or blades and other moving parts of the shutter are made to be very light. In addition, in order to maximize the quickness of the solenoid action, typically the current to the solenoid coil is briefly increased to a level that, if sustained, could damage the coil. The combination of light construction and quick action associated with prior art industrial shutters results in the production of undesirable vibration and noise. In addition, while such shutters can produce short bursts of operation at frequencies above 20 Hertz, they are susceptible to overheating and failure if operated for extended periods at or near their optimum rate. Due to the light construction, these units fail frequently and, in order to obtain light but strong construction the components are typically spot-welded together, making repairs impractical. To avoid bouncing at the end of an opening or closing stroke and to reduce vibration and wear, mechanical dampers are employed. A typical damper comprises a bumper made of rubber or plastic attached at the end of a spring. Such dampers are subject to wear, requiring frequent replacement, and can stick to the shutter blade.
Solenoid shutters rely on a return spring to move the shutter vane to its resting position when current to the solenoid is removed. The action of the return spring is much slower than the solenoid. Accordingly, two versions of such shutters are normally made, normally open and normally closed. In order to provide a shutter which is equally fast opening and closing it would be necessary to use two solenoids, increasing the cost and complexity of the device.